1. Field of the Invention
The present invention relates to a control of a machine such as a machine tool, a manufacturing machine and a robot, having a plurality of operational elements, and more particularly to a synchronous control for synchronously driving the operational elements of the machine.
2. Description of Related Art
In control of a machine, such as a machine tool, a manufacturing machine and a robot, having a plurality of operational elements, there is a case where some operational elements are required to be synchronously controlled. In such synchronous control, there is known a synchronous control method in which a leading element and a follower element are designated in the operational elements and the follower element is position-controlled based on position data of the leading element. This synchronous control is known as a synchronous control of “electronic cam” in which variations of positions of the leading element and the follower element are repeated periodically in synchronism. The follower element is connected with a drive system including a drive source such as a servomotor and is position-controlled based on position data of the leading element. With this synchronous control, the follower element operates in synchronism with the leading element.
FIG. 11 is a schematic diagram showing a conventional synchronous control system. In FIG. 11, a servomotor of a follower drive system 2 is driven based on motion commands from a controller 6. The controller 6 stores data on a positional relationship between a leading element of a leading drive system 1 and a follower element of the follower drive system 2 moving in synchronism with each other, obtains position data of the follower element based on the stored positional relationship in synchronism and the position data of the leading element at every predetermined period, and provides motion commands to the follower drive system 2 for driving the follower element based on the obtained position data of the follower element, to thereby position-control the follower element. In this way, the follower element 2 is controlled in synchronism with the leading element 1.
In the conventional synchronous control, there may be produced a large mechanical shock when the follower element which stands still is brought into synchronism with the leading element which is in motion, and therefore velocity of the leading element has to be reduced.
In the conventional synchronous control, for example, the follower element is position controlled to reduce a deviation between a present position of the follower element and a synchronized position when starting motion of the follower element. By this position control, the follower element moves to the synchronized position and reached a synchronized velocity. However, an acceleration of the follower element when it reaches the synchronized position and an acceleration of the follower element required at the synchronized position are much different in direction. As a result, a large mechanical shock is caused in the drive mechanism of the follower element.